In general, polyesters such as polyethylene terephthalate have excellent mechanical and chemical characteristics and are, therefore, used in a wide range of applications such as those films for magnetic recording media, general industry, heat-sensitive stencil plates, ribbons, reflecting plates, optics, food packings, paper alternatives, mold-release, electric insulation and capacitors.
Particularly, in recent years, attention has been drawn to photovoltaic power generation which is expected to contribute to CO2 reduction; and, in a film for solar battery, there is a demand for an improvement in the hydrolysis resistance, which is one of the required properties, and a reduction in the cost.
As a method of improving the hydrolysis resistance, it is known to perform solid phase polymerization so as to reduce the amount of terminal carboxyl groups. In Patent Document 1, it is described that an electrical insulating film is subjected to solid phase polymerization so as to reduce the cyclic trimer content.
Further, in Patent Documents 2 and 3, it is proposed to further add ethylene glycol during or after esterification reaction.
Moreover, Patent Document 4 proposes a polyester for lamination to a metal plate in which the amount of terminal methoxy groups is reduced.